Views & Templates
ERB conventions for vanilla Rails applications.
Partial Organization
Lowest common ancestor - place partials at the highest shared directory:
# Shared by cards/show and cards/index
app/views/cards/_card.html.erb
# Shared across controllers
app/views/application/_flash.html.erb
# Display variants of same model
app/views/cards/display/_compact.html.erb
app/views/cards/display/_full.html.erb
Never create deeply nested partials only used in one place.
Optional Locals
Use local_assigns.fetch with explicit defaults:
<%# Good - explicit default, raises if required %>
<% pinned = local_assigns.fetch(:pinned, false) %>
<% card = local_assigns.fetch(:card) %>
<%# Bad - silent nil, ambiguous intent %>
<% pinned = local_assigns[:pinned] || false %>
CSS Class Helper
Build classes with array + compact + join:
<%# Good %>
<div class="<%= [
'card',
('card--pinned' if card.pinned?),
('card--closed' if card.closed?)
].compact.join(' ') %>">
<%# Bad - string interpolation %>
<div class="card <%= 'card--pinned' if card.pinned? %>">
For complex cases, use token_list helper:
<div class="<%= token_list('card', 'card--pinned': card.pinned?) %>">
Collection Rendering
Always cache, always specify as::
<%= render partial: 'cards/card',
collection: @cards,
as: :card,
cached: true %>
Turbo Streams
Prepend/append with update for empty states:
<%# Add item and update counter/empty state %>
<%= turbo_stream.before :cards, @card %>
<%= turbo_stream.update :cards_count, @cards.count %>
<%# Remove and handle empty %>
<%= turbo_stream.remove @card %>
<%= turbo_stream.update :cards_empty, partial: 'empty' if @cards.none? %>
Stimulus Integration
Layer controllers on existing elements:
<%# Good - multiple controllers on body %>
<body data-controller="keyboard shortcuts dropdown">
<%# Bad - wrapper div just for controller %>
<div data-controller="card-actions">
<%= render @card %>
</div>
Keyboard shortcuts via body controller:
<body data-controller="keyboard"
data-action="keydown->keyboard#handle">
Quick Reference
| Pattern | Use |
|---|---|
local_assigns.fetch(:x, default) | Optional locals |
[...].compact.join(' ') | Conditional CSS classes |
cached: true, as: :item | Collection rendering |
turbo_stream.before + .update | Add + refresh related |
data-controller="a b c" | Multiple controllers |
Common Mistakes
| Wrong | Right |
|---|---|
local_assigns[:x] || default | local_assigns.fetch(:x, default) |
| Wrapper div for Stimulus | Add controller to existing element |
render @cards without cache | render collection:, cached: true |
| Partial in deep nested path | Lowest common ancestor |